1. Field of the Invention
The present invention relates to input devices capable of detecting, on the basis of a change in the electrostatic field between electrodes, a position to which an operating unit is placed in close proximity, and more particularly, to a low-profile input device having a shielding function.
2. Description of the Related Art
Examples of input devices for inputting coordinate data to be used for moving a cursor displayed on the screen of a personal computer or the like are planar input devices utilizing a change in electrostatic capacitance.
In a planar input device, a plurality of X electrodes and a plurality of Y electrodes are arranged in a matrix and the plurality of X electrodes and the plurality of Y electrodes face each other with an insulating layer therebetween. When one of the X electrodes is selected and a voltage is applied between the selected X electrode and each of the Y electrodes, the rising of the voltage depends on the electrostatic field between the selected X electrode and each of the Y electrodes. When a finger, which is a conductive material, is placed in close proximity to the selected X electrode, electrostatic capacitance is generated between the finger and the selected X electrode. Thus, rising of the voltage between the selected X electrode, to which the finger is placed in close proximity, and each of the facing Y electrodes varies in accordance with a change in the electrostatic field. When a change in the rising of the voltage is detected, the position of the planar input device at which an operation is performed can be identified.
In a case where transparent substrates and transparent electrodes are used in a planar input device of this type and such a planar input device is provided in front of a display unit, such as a liquid crystal display device, a user is able to touch the display screen, while looking at the contents displayed on the display unit, to input an operating signal.
However, since a display unit, such as a liquid crystal display device, is driven at a high frequency, radiation noise is likely to occur in the display unit. If a planar input device is disposed in the vicinity of such a display unit, the potential of an electrode of the planar input device is susceptible to variation due to the influence of radiation noise. Since planar input devices are used to detect fine variations in the intensity of the electrostatic field between electrodes, in a case where an electrode potential varies due to the influence of radiation noise, a malfunction is likely to occur in detection of the position touched by a finger.
Under such circumstances, in the case of disposing a display unit on a planar input device, it is necessary to form a shielding layer, which is formed of a transparent conductive film, between the planar input device and the display unit. However, in order to form a transparent shielding layer on one surface of a substrate and form a transparent electrode on the other surface of the substrate, it is necessary to process a substrate having transparent conductive layers, such as indium tin oxide (ITO) films, on both surfaces thereof. Thus, a manufacturing process is problematic. Furthermore, a very high cost is required for the manufacturing. Thus, in order to manufacture a planar input device of this type, at least three substrates, that is, a transparent substrate including a shielding layer, a transparent substrate including X electrodes, and a transparent substrate including Y electrodes, must be stacked on each other. As a result, the total thickness of the substrates becomes large, and it is difficult to use such a thick planar input device for a low-profile apparatus.
Examples of the related art include Japanese Unexamined Patent Application Publication Nos. 11-85371 and 2002-366304.